BOOKS AND CURRENT LITERATURE 93 



administration of the National Forests so efficient, and the enthusiastic 

 devotion of its men, which has done so much to win public respect for 

 our national forest policy. It is fine to have such a well executed 

 and amply illustrated hook for the dissemination of sound information 

 about our National Forests. — Forrest Shreve. 



A Recent Study of Club Root. — Kunkel's recent work 1 on Plas- 

 modiophora disproves the idea so widely prevalent that infection of 

 cabbage plants must occur through the root hairs. In his experiments 

 paper cylinders were fastened around the roots of healthy plants after 

 the latter had been washed free from earth, at places free from branches. 

 The cylinders were then filled with earth containing the spores of 

 Plasmodiophora and sealed with paraffin, the roots were covered with 

 moist earth, and the plants were examined at the end of two weeks. 

 Infection always occurred within the cylinders regardless of the loca- 

 tion on the root, and in no case did it arise outside. The experiment 

 appears to demonstrate clearly that the parasite can enter tissue far 

 back of the root-hair region. Supplementary study of prepared slides 

 revealed the parasite below the root hairs in the root-tip in some of his 

 material. Stems were also found to be capable of infection. Two 

 thousand plants varying in age from one to twelve months were in- 

 oculated in the stem, and infection followed in every one. Cells be- 

 come infected by host cell division and by penetration of the parasite 

 through the wall of an infected cell into normal ones. Nuclei respond 

 to the stimulus of the parasite by a greater proportional enlargement 

 than the cytoplasm shows, and this response is evident in cells at a 

 considerable distance from the infected spot. The club root is first 

 noticeable as a slight swelling in about eleven days, but two weeks are 

 required before the cambium is penetrated. The mass of parasitic 

 protoplasm bears a remarkably constant ratio to that of the host. 

 Wilting of the host is due to hypoplasia of xylem, and to the splitting 

 of the woody cylinder caused by the infection and growth of the medul- 

 lary rays. — J. G. Brown. 



1 Kunkel, L. O. Tissue Invasion by Plasmodiophora Brassicae. Jour. Agric. 

 Res. 14: 543-572: pi. 20. 1918. 



